Phylum Mollusca Ex: Chitons, Snails, Clams, Octopods, and Squid. - ppt download Presentation is loading. Please wait. Phylum Mollusca Ex: Chitons, Snails, Clams, Octopods, and Squid. Published by Damian Robinson Modified about 1 year ago Embed Presentation on theme: "Phylum Mollusca Ex: Chitons, Snails, Clams, Octopods, and Squid."— Presentation transcript: 1 2 Phylum Mollusca Ex: Chitons, Snails, Clams, Octopods, and Squid 3 General Characteristics It is believed that the molluscs evolved from annelids, but some scientists argue that they may have evolved from flatworms. 50% of the species are marine. 4 General Characteristics Body Plan Soft bodied (term Mollusca is Latin for “soft”) invertebrates with bilateral symmetry. Usually protected by a calcareous shell. 5 General Characteristics Body Plan Unsegmented body with a reduced coelum. The soft body parts are protected by a protective tissue called the mantle.

6 General Characteristics Body Plan They possess a mantle cavity where the gills are located, into which the anus and kidneys release excretia, and into which eggs and sperm are released. 7 General Characteristics Body Plan Two major parts: Head-foot: contains head, mouth, sensory organs, and muscular foot. 8 General Characteristics Body Plan Visceral Mass: contains other organ systems, including circulatory, digestive, respiratory, excretory, and reproductive systems. (#4 is visceral mass) 9 General Characteristics Most possess a radula. A ribbon of tissue that contains teeth. The radula is used for scraping, tearing, piercing, or cutting food. 10 General Characteristics The shell is secreted (made) by the mantle. The shell consists of 3 layers: Periostracum: outer Prismatic: middle Nacreous: inner 11 Class Polyplacophora “Many plates” Chitons Live in the rocky intertidal zone. Retain the greatest number of ancestral characteristics. 12 Class Polyplacophora Shell: 8 overlapping plates held together by a tough girdle formed from the mantle. Foot used for attaching tightly to rocks.

13 Class Polyplacophora They possess a radula with teeth that are mineralized with magnetite. Magnetite may become magnetized and the chitons may use the magnetic field of the earth to navigate (like a compass). 14 Class Scaphopoda “Sheath foot” Tusk shells: shell resembles an elephant tusk with 2 openings. Foot protrudes from one end and is used for burrowing 15 Class Scaphopoda Water enters and exits small end to exchange gases and remove waste. The foot or special tentacles emerge from the other end to feed on foramniferans. 16 Class Gastropoda “Stomach foot” 75% of Mollusc species are Gastropods Great diversity Most are found on the benthos both on rocky and soft bottoms. 17 Class Gastropoda The Shell Typically a pointed tube or cone into which the animal can contract. The opening can be closed with a cover called the operculum. Operculum---- 18 Class Gastropoda Nudibranchs A subgroup of Molluscs that have lost all traces of a shell. 19 Class Gastropoda The Foot Broad and mucus covered.

May function as an adhesive gland that works like a suction cup. 20 Class Pelecypoda or Bivalvia “Hatchet foot” Ex: Clams, Oysters, Mussels, Scallops. Typically sessile, living burrowed in sandy or muddy sediments. 21 Class Pelecypoda The Shell Consists of 2 valves (plates) that generally completely cover the body, and are connected at a hinge by ligaments. They possess no head or radula. Filter feeders. 22 Class Pelecypoda The Foot Used primarily for burrowing and anchoring. 23 Class Pelecypoda Formation of Pearls An irritant (Usu. a grain of sand) comes between the shell and the mantle tissue. The response is to cover it with layers of nacreous material. If the irritant is spherical and embeds in the mantle tissue it becomes a pearl. 24 Class Cephalopoda Ex: Squid, Octopus, Nautilus, Cuttlefish 25 Class Cephalopoda “Head foot” Most advanced class of Molluscs. Have a highly developed brain and sense organs.

26 Cephalopoda The eyes are very much like vertebrate eyes and are the dominant sense organ. 27 Cephalopoda The Foot Modified into a head- like structure with a ring of tentacles surrounding the mouth. The tentacles are used for capturing prey, defense, reproduction, and in some cases locomotion. 28 Cephalopoda The Foot Part of the foot is modified into a siphon used in jet propulsion. Ink can be expelled from the siphon to distract and confuse predators. 29 Cephalopoda They are the largest of the invertebrates. Architeuthus: the giant squid can reach lengths of 60 ft. 30 Cephalopoda The Shell With the exception of Nautilus they all have lost the heavy external shell. Squid have a small internal shell called the Pen, and octopi have no shell. 31 Cephalopoda Color Change Cephalopods communicate through movements and color change. Color change involves specialized cells called chromatophores. 32 Cephalopoda Feeding They are active carnivores. The radula is reduced. They have a pair of jaws shaped like the beak of a parrot.

tmb.edu/viddb/vidsrch 2.cfm tmb.edu/viddb/vidsrch 2.cfm 33 ****The End**** 10 Facts About Mollusks 10 Facts About Mollusks Sign Up for Our Free Newsletters Thanks, You're in! What I Learned About Today You might also enjoy: Health Tip of the Day Recipe of the Day There was an error. Please try again. Please select a newsletter. Please enter a valid email address. Did you mean ? Mollusks (Phylum Mollusca) Characteristics and Facts By Jennifer Kennedy Updated August 29, 2016. Mollusca is a taxonomic phylum that contains a diverse array of organisms (referred to as ' mollusks '), and the taxonomic classes that include snails, sea slugs, octopuses, squid, and bivalves such as clams, mussels and oysters. From 50,000 to 200,000 species are estimated to belong to this phylum. Imagine the obvious differences between an octopus and a clam, and you'll get an idea of the diversity of this phylum!

Mollusk Characteristics: Characteristics common to all mollusks: They have a soft body They have a usually distinguishable 'head' and 'foot' region. They use their muscular foot to move. Some may have a hard covering, or exoskeleton. They have a heart that pumps blood through their blood vessels, digestive system, and a nervous system. Classification: Phylum: Mollusca Feeding: Many mollusks feed using a radula , which is basically a series of teeth on a cartilage base. The radula can be used for complex tasks, from grazing on marine algae or drilling a hole in another animal's shell. continue reading below our video 4 Tips for Improving Test Performance Reproduction: Some mollusks have separate genders, with males and females represented in the species. Others are hermaphroditic (reproductive organs associated with both male and female). Distribution: Mollusks may live in salt water, in fresh water, and even on land. Conservation & Human Uses: Thanks to their ability to filter large quantities of water, mollusks are important to a variety of habitats. They are also important to humans as a food source, and have been historically important for making tools and jewelry.

Sources: Snails, slugs, clams, squids, and octopi Latin mollus: “soft” 2nd Largest animal phylum on Earth ~ 150, 000 known species CLIP. - ppt download Download Presentation is loading. Please wait. Snails, slugs, clams, squids, and octopi Latin mollus: “soft” 2nd Largest animal phylum on Earth ~ 150, 000 known species CLIP. Published by Misael Radway Modified about 1 year ago Embed Similar presentations More Presentation on theme: "Snails, slugs, clams, squids, and octopi Latin mollus: “soft” 2nd Largest animal phylum on Earth ~ 150, 000 known species CLIP."— Presentation transcript: 1 snails, slugs, clams, squids, and octopi Latin mollus: “soft” 2nd Largest animal phylum on Earth ~ 150, 000 known species CLIP 2 Almost all habitats Soft-bodied animals, usually with a hard external shell (Calcium containing). Some have lost the shell completely.

CLIP 3 Most mollusks are marine, though some inhabit fresh water, and some snails and slugs live on land. Mollusks are soft-bodied animals, but most are protected by a hard shell of calcium carbonate. –Slugs, squids, and octopuses have reduced or lost their shells completely during their evolution. 4 Protostome coelomates - 3 main body parts: Foot, Mantle, Visceral Mass the coelom is reduced and limited to region around heart 5 foot (typically for locomotion), a visceral mass with most of the internal organs, and a mantle. –The mantle, which secretes the shell, drapes over the visceral mass and creates a water-filled chamber, the mantle cavity, with the gills, anus, and excretory pores. –Many mollusks feed by using a straplike rasping organ, a radula, to scrape up food. 6 Body Plan: Foot: -Flat: crawling -Spade-shaped: burrowing -Tentacles: capturing prey Mantle: Mantle: thin layer of tissue that covers the body.

Visceral mass - contains internal organs: Water intake and output 7 Feeding: Can be herbivores, carnivores, filter feeders, detritivores, or parasites. 8 Respiration: Aquatic-Gills through diffusion Blue hemocyanin, not hemoglobin, is respiratory pigment Has copper instead of iron Land- mantal cavity lined with blood vessals- diffusion Must be kept moist 9 Circulation: Open circulatory system with blood-filled spaces called hemocoels a heart pumps hemolymph through vessels into a hemocoel 10 Excretion: nephridia Movement: Mucus Jet propulsion rapid clapping of valves releases water in spurts 11 Reproduction: Sexual- -external fertilization (Snails) - internal fertilization (tentacled) - hermaphrodites 12 13 1-Polyplacophore Chitons are marine animals with oval shapes and shells divided into eight dorsal plates. Chitons use their muscular foot to grip the rocky substrate tightly and to creep slowly over the rock surface. Chitons are grazers that use their radulas to scrape and ingest algae.

Four main classes: 14 2 -Bivalva: clams, scallops, mussels Have 2 shells held together by adductor muscles that close the shell tightly to protect the animal. Feed by filtering small particles from the water sedentary, attached to hard surface foot used for digging in sand 15 Mantle cavity contains gills - feeding and gas exchange. Filter feeders –Cilia convey the particles to the mouth. –Water flows into mantle cavity via the incurrent siphon, passes over the gills, and exits via the excurrent siphon. Sexes are separate; the gonad is located around coils of intestine 16 Most bivalves live rather sedentary lives. –Sessile mussels secrete strong threads that tether them to rocks, docks, boats, and the shells of other animals. –Clams can pull themselves into the sand or mud, using the muscular foot as an anchor. –Scallops can swim in short bursts to avoid predators by flapping their shells and jetting water out their mantle cavity.

17 3-Gastropoda: “univalves”: snails and slugs -Greek gaster: “stomach” -Single shell in snails -Can close “door” if threatened Move by muscular contractions of the single foot Slugs have either a reduced shell or no shell at all Use a radula for feeding 18 Most are marine, but there are also many freshwater or terrestrial species. In place of the gills found in most aquatic gastropods, the lining of the mantle cavity of terrestrial snails functions as a lung. 3-Gastropoda: Aquatic gastropod gills are in the mantle cavity respiratory pores 19 Land snails are hermaphroditic. a. In pre-mating behavior, they meet and shoot calcareous darts into each other's body wall. b. Each inserts a penis into the other's vagina; this provides sperm for future fertilization. c. Eggs are deposited in soil and development proceeds without formation of a larvae. 20 Hermaphroditism assures that any two animals can mate-very useful in slow-moving animals 21 Some species are predators.

–Radula is modified to bore holes in the shells of other organisms or to tear apart tough animal tissues. –The tropical marine cone snails, teeth on the radula form separate poison darts, which penetrate and stun their prey, including fishes. 22 4- Cephalopoda: “head-foot mollusks”: cuttlefish, squids and octopuses Giant squid can reach 4400 lbs.!! -Very active and can be fast swimmers -reduced shell or no shell -tentacles are modified foot -move by “jet propulsion” -Can have large eye 23 Cephalopods use rapid movements to dart toward their prey which they capture with several long tentacles. Squids and octopuses use beaklike jaws to bite their prey and then inject poison to immobilize the victim. A mantle covers the visceral mass, but the shell is reduced and internal in squids, missing in many octopuses, and exists externally only in nautiluses. 24 Squids and octopuses possess ink sacs; they squirt a cloud of ink to escape predators.

25 A squid has three hearts, one pumps blood to internal organs; two pump blood to gills 26 Octopuses and squids move by "jet propulsion", sucking water into a muscular sac in the mantle cavity surrounding their bodies and quickly expelling it out a narrow excurrect siphon. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Cephalopods have an active, predaceous lifestyle 27 Squid- Pen 28 CLIP The mollusca The Mollusca A cuttlefish, a coleoid cephalopod, moves primarily by undulating its body fins. Mollusca is one of the most diverse groups of animals on the planet, with at least 50,000 living species (and more likely around 200,000). It includes such familiar organisms as snails, octopuses, squid, clams, scallops, oysters, and chitons.

Mollusca also includes some lesser known groups like the monoplacophorans , a group once thought to be extinct for millions of years until one was found in 1952 in the deep ocean off the coast of Costa Rica. Molluscs are a clade of organisms that all have soft bodies which typically have a "head" and a "foot" region. Often their bodies are covered by a hard exoskeleton, as in the shells of snails and clams or the plates of chitons. A part of almost every ecosystem in the world, molluscs are extremely important members of many ecological communities. They range in distribution from terrestrial mountain tops to the hot vents and cold seeps of the deep sea, and range in size from 20-meter-long giant squid to microscopic aplacophorans , a millimeter or less in length, that live between sand grains. These creatures have been important to humans throughout history as a source of food, jewelry, tools, and even pets. For example, on the Pacific coast of California, Native Americans consumed large quantities of abalone and especially owl limpets.

However, the impact of Native Americans on these molluscan communities pales by comparison to the overharvesting of some molluscan taxa by the United States in the 1960s and 1970s. Species whose members once numbered in the millions, now teeter on the verge of extinction. For example, fewer than 100 white abalone remain after several million individuals were captured and sold as meat in the 1970s. Besides having yummy soft parts, molluscs often have desirable hard parts. The shells of some molluscs are considered quite beautiful and valuable. Molluscs can also be nuisances, such as the common garden snail; and molluscs make up a major component of fouling communities both on docks and on the hulls of ships. On the left is a marine snail, the California Trivia (Trivia californiana). Here the mantle covers much of the shell. Note how a portion of the mantle is rolled into a tube shape to form the siphon just above the head. At the right is a restoration of one of the largest of all molluscs, the Giant Squid (Architeuthis).

They also have a very long and rich fossil record going back more than 550 million years, making them one of the most common types of organism used by paleontologists to study the history of life. Systematics Molluscan systematics are still in flux. As you can see from the cladogram below, there is still no agreement on some of the major relationships. The polytomies shown indicate that the question of which molluscs are the most closely related is still a matter of debate. However, new types of data and much larger and more sophisticated analyses continue to be performed. The resolved relationships shown (such as cephalopods, scaphopods, and gastropods) are recent discoveries. Visit the mollusca pages on the Tree of Life for more on molluscan systematics. Morphology Despite their amazing diversity, all molluscs share some unique characteristics that define their body plan. The body has a head, a foot and a visceral mass. This is all covered with a mantle (also known as a pallium) that typically secretes the shell.

In some groups, like slugs and octopuses, the mantle is secondarily lost, while in others, it is used for other activities, such as respiration. The freshwater Sinistral Pond Snail (Physella sp.) scrapes algae from the glass with its radula, the two "toothy" arcs you can see lining the mouth. Click on the photo for a closer look. The buccal cavity, at the anterior of the mollusc, contains a radula (lost in bivalves)  a ribbon of teeth supported by an odontophore, a muscular structure. The radula is generally used for feeding. The ventral foot is used in locomotion. This foot propels the mollusc by utilizing muscular waves and/or cilia in combination with mucus. Typically, at least in the more primitive members of each group, there are one or more pairs of gills (called ctenidia) which lie in a posterior cavity (the pallial cavity) or in a posterolateral groove surrounding the foot. The pallial cavity typically contains a pair of sensory osphradia (for smelling) and is the space into which the kidneys, gonads, and anus open.

Molluscs are coelomate, although the coelom is reduced and represented by the kidneys, gonads, and pericardium, the main body cavity which surrounds the heart. Life history and ecology Molluscs occur in almost every habitat found on Earth, where they are often the most conspicuous organisms. While most are found in the marine environment, extending from the intertidal to the deepest oceans, several major gastropod clades live predominantly in freshwater or terrestrial habitats. Remarkably, one study found around 3000 species within a single locality at a coral reef in New Caledonia. In terrestrial communities, gastropods can achieve reasonably high diversity and abundance: as many as 60-70 species may coexist in a single habitat and abundance in leaf litter can exceed more than 500 individuals in four liters of litter. Many marine molluscs emerge from their eggs as planktonic trochophore larvae, however, Sinistral Pond Snails (Physella sp.) emerge from their eggs as young snails. The whitish, jellybean-shaped organisms are ostracodes (crustaceans).

Marine molluscs occur on a large variety of substrates including rocky shores, coral reefs, mud flats, and sandy beaches. Gastropods and chitons are characteristic of these hard substrates, and bivalves are commonly associated with softer substrates where they burrow into the sediment. However, there are many exceptions: the largest living bivalve, Tridacna gigas, lives on coral reefs, and many bivalves (e.g., mussels and oysters) attach themselves to hard substrates. Some microscopic gastropods even live interstitially between sand grains. Large concentrations of gastropods and bivalves are found at hydrothermal vents in the deep sea. Living in these or other dysoxic habitats appears to be a plesiomorphic condition for the Mollusca and several outgroups . For example, the fauna of Palaeozoic hydrothermal vent communities includes the molluscan groups Bivalvia , Monoplacophora and Gastropoda as well as the outgroups Brachiopoda and Annelida. The adoption of different feeding habits appears to have had a profound influence on molluscan evolution.

The change from grazing to other forms of food acquisition is one of the major features in the radiation of the group. Based on our current understanding of relationships, the earliest molluscs grazed on encrusting animals and detritus. Such feeding may have been selective or indiscriminate and will have encompassed algal, diatom, or cyanobacterial films and mats, or encrusting colonial animals. Truly herbivorous grazers are relatively rare and are limited to some polyplacophorans and a few gastropod groups. Most chaetodermomorph aplacophorans, monoplacophorans and scaphopods feed on protists and/or bacteria while neomeniomorph aplacophorans graze on cnidarians. Cephalopods are mainly active predators as are some gastropods, while a few chitons and septibranch bivalves capture microcrustaceans. Most bivalves are either suspension or deposit feeders that indiscriminately take in particles, but then elaborately sort them based on size and weight, typically assimilating bacteria, protists, and diatoms.

The fossil record The Mollusca include some of the oldest metazoans known. Late Precambrian rocks of southern Australia and the White Sea region in northern Russia contain bilaterally symmetrical, benthic animals with a univalved shell ( Kimberella ) that resembles those of molluscs. The earliest unequivocal molluscs are helcionelloid molluscs that date from Late Ediacaran (Vendian) rocks. In the Early Cambrian the Coeloscleritophora are also present. Most of the familiar groups, including gastropods, bivalves, monoplacophorans, and rostroconchs, all date from the Early Cambrian, whereas cephalopods are first found in the Middle Cambrian, polyplacophorans in the Late Cambrian, and the Scaphopoda in the Middle Ordovician . Most of these early taxa tend to be small (10 mm in length). The Late Vendian-Early Cambrian taxa bear little resemblance to the Cambrian-Ordovician taxa (most of which remain extant today).

On the left is Inoceramus sp., a bivalve from the Cretaceous of Alameda County, CA. At right is Turritella andersoni, a gastropod from the Eocene of Ventura County, CA. After their initial appearance, molluscan taxonomic diversity tended to remain low until the Ordovician, when gastropods, bivalves, and cephalopods show large increases in diversity. For bivalves and gastropods this diversification increases throughout the Phanerozoic, with relatively small losses at the end-Permian and end-Cretaceous extinction events. Cephalopod diversity is much more variable through the Phanerozoic, whereas the remaining groups (monoplacophorans, rostroconchs, polyplacophorans, and scaphopods) maintain low diversity over the entire Phanerozoic or became extinct. Original text by Paul Bunje, 2003. Photos of cuttlefish, California Trivia, Giant Squid, Sinistral Pond Snail radula and eggs, all © Larry Jon Friesen .

Photos of Inoceramus and Turritella andersoni by Sarah Rieboldt, © UCMP. Mollusca phylogeny based on Sigwart, J.D., and M.D. Sutton. 2007. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proceedings of The Royal Society B 274(1624):2413-2419; and suggestions from Gonzalo Giribet, Harvard University. * there are 600 species in 40 genera * all are marine * the single most distinctive characteristic of chitons is the presence of 8 overlapping dorsal transverse plates * the mantle or pallium is responsible for laying down the plates * in some species the mantle covers parts of the plates while in Cryptochiton the mantle completely covers the plates * all species have a very highly developed foot which is used to attach to the surface of the substrate * because of this they require a solid substrate and usually don't live in sandy or muddy habitats * mostly found in tidal zones * these have the ability to stay out of the water for a long period of time (ie.

during low tide) * the foot attaches so tightly to substrate it traps water in and around the gills with enough oxygen to sustain them until tide comes in again * during this time they are inactive * foot is also used for locomotion * because of this life style they are all raspers and scrapers; feeding on periphyton * some feed on dead or decaying organisms * all have a well developed radula * Respiration * is accomplished by gills located in pallial groove * Circulation * heart is at the posterior end of body consisting of a ventricle and a pair of auricles * there is a single aorta (ie.

dorsal blood vessel) that pushes water anteriorly * blood is taken to organs and into gills where it gets oxygenated before it returns to the auricles * Excretion * accomplished by a pair of large nephridia * each open to outside by a nephridiopore near the posterior gills * Nervous System * function not well understood but may be able to sense light * Reproduction * all are dioecious * each have a single gonad that opens to outside by a large pair of gonopods- not associated with nephridia * eggs and sperm extruded to outside; fertilization is external * in some species the sperm is taken into mantle cavity where eggs are fertilized * there is a free-living trochophore larva * some females brood young; there is no larva produced in those species * from trochophore development is direct * About 250 species * all are marine * they are unique as molluscs since they lack a shell or plates and have no foot * they more resemble worms than molluscs * they do have a radula * most are deep sea dwellers and burrow into substrate * are predators or scavengers * are either monoecious or dioecious * very

 little is known of their biology * less is known of their exact relationship with other molluscs * they were removed from the chitons (Class Amphineura) in 1978 SNAILS AND SLUGS * largest and most diversified group of molluscs * includes some of the most primitive living molluscs (marine species) to some highly evolved terrestrial air breathing slugs and snails * single most characteristic feature of the gastropods is torsion * the visceral mass and mantle have become 180 degrees * has nothing to do with the coiling of the shell; some gastropods are not coiled, but all undergo torsion * the twisting of the body has caused: * mantle to be moved anteriorly behind the head * there is a reduction of organs on the right side of the body * adults are not bilaterally symmetrical- for example right gonads reduced or lost * 2 pairs of tentacles; eyes at end of posterior tentacles * some species have great reduction or loss of shell; these are the slugs * In both the Opistobranchs and pulmonates there is tendency for loss of larval forms, and a reduction of torsion; reduced to about 90 degrees

 * TORSION * Involves the twisting of all internal organs into a loop * It is thought that torsion was actually developed as an adaptation for the larval stage of gastropods * in pretorsion condition the larva as it withdrew into shell the foot went first, then the velum then the head- the head comes in last * after the torsion the head and velum are retracted first and the foot is retracted last * this may therefore be a protective devise to protect the head * torsion by and large is a disadvantage for the adult since it is accompanied by a loss or great reduction of the organs of the right side * so those organs are non-functional * this can develop problems: * and locomotion * in gill breathers, however, there is a certain amount of advantage to torsion * the inhalant siphon is anterior due to position of mantle; allows water to be taken from the front of snail * also sense organs of the mantle are moved anteriorly with torsion and allows them to be added to those of the head region * osphradium, along with tentacles and eyes are all anterior * all in all the great success of the gastropods is evidence that although torsion may be

 a slight disadvantage in adulthood; those disadvantages have been overcome * LOCOMOTION- there are 4 primary ways * Foot - movement by the foot; various wave-like peristaltic movements cause gastropods to creep along due to muscular contraction * Ciliary Action - cilia at bottom of foot; especially in small species that live on sand and mud bottoms * Operculum - those that have operculum use it by extending and anchoring it and foot contracts and pulls animal along; also used to dig * Swimming - by the use of extensions of the foot (fins) also called parapodia; best developed in opisthobranchs such as sea hares, sea butterflies * NUTRITION- * All gastropods have a radula and it is used for feeding; it is modified from one group to the next depending on the type of feeding that is involved * more primitive condition is that the radula is composed of several transverse rows of teeth which is used for rasping * in more advance gastropods, especially neogastropods, the radula is modified for predation * have radula consists of long sharp, barb-like teeth * in some cones radula developed into a harpoon-like structure used

 to inject venom into prey * gastropods are found in all parts of the food chain: * Hervivores - found in all classes * feed on algae; rasping it off the substrate or may feed on the softer tissues of plants, using the radula to shred the food * one group has a very specialized radula able to slice open individual algal cells and suck out protoplasm * Carnivores - mostly the prosobranchia and opisthobranchia * very few pulmonates are carnivores * radula is modified for cutting, grasping and tearing and scraping * most have a highly developed extensible proboscis which can be used to suck juices from prey * some like the nudibranchs are grazing carnivores; feeding on sessile animals such as coral, sea anemones, bryozoans, sponges * no proboscis here, but sometimes there is a jaw used to cut tissue from prey * Scavengers and Deposit Feeders- feed primarily on dead and decaying organisms or on detritus * may have a proboscis that enables them to suck up detritus off the bottom * Suspension Feeders (Filter Feeders)- primarily feed on plankton * food is

 carried in by inhalant current over gills * gills secrete a sticky substance trapping food * in these the radula is usually very reduced; in a few species it seems to be lost * there is usually a well developed ciliary system in the gills and proboscis to transport trapped food to mouth * EXCRETION AND WATER BALANCE * Many archeogastropoda have 2 nephridia, but in all others the right one has disappeared or is very reduced and functions in reproduction only * because of torsion nephridia are located anteriorly in visceral mass * nephridia are sac-like structures that usually open into mantle cavity and wastes are removed by water currents * in pulmonates this is not possible because mantle cavity forms a lung so ureter is elongate and opens to front of mantle near the anus and pneumostome * freshwater species have to get rid of excess water so nephridia transport lots of water to outside * terrestrial species are not good at conserving water, because of this terrestrial snails are restricted to living in habitats where relative humidity is very high, such as beneath logs or rocks, on forest floors etc.

* because of torsion heart is anterior in the visceral mass * in primitive archaeogastropods there are two auricles, * in all other gastropods the right auricle has become vestigial or lost (fig.

11-40, page 382 gives a diagram of typical circulation of blood in snail) * the mantle as in all molluscs secretes the shell * it is three lobed and middle lobe shows greatest development of sense organs * the shells or valves are not really 2 separate entities as many textbooks report * the early development is similar to the discussion in the scaphopods * in the development of the shell laid down by the dorsal extension of mantle or mantle isthmus secretes less crystalline calcium carbonate and more elastic tanned proteins than the rest of the mantle and in that area the ligament is formed * the ligament is elastic and functions as a hinge which is opened and closed by a large set of muscles (the adductors) * when adductors relax the tension of the ligament opens the valves * Shell itself is composed of three layers: * Periostracum Layer or horny outer layer- calcareous layer composed of aragonite and calcite * Prismatic Layer- middle layer of crystalline calcium carbonate * Nacre- the inner pearly layer; calcium carbonate laid in sheets * shell is composed of up to 72% of weight of animal * pearls produced by all bival

ves caused by sand grains or something else trapped between mantle and nacre * irritation causes mantle to secrete nacrous layers around sand grains to forms pearls * middle fold of mantle contains most of the sense organs * many species have pallial tentacle (ie.

scallops) which contain tactile and chemoreceptor cells * Statocysts- usually found in foot; function in orienting animal; are lacking or reduced in sessile forms * Ocelli- found in some mobile species such as scallops * Osphradium- chemoreceptor used for food detection * REPRODUCTION * there is no copulation but fertilization is almost exclusively internal * sperm is shed to outside and brought in by females * in marine forms after fertilization larvae are shed to environment- typical trochophore larva develops to veliger that then drops to bottom and develops into adult * in freshwater forms (Unionidae) there are larvae produced called glochidia * are shed into water and attach to a host (fish or amphibian); place of attachment usually gills or skin * many species are host specific * in Lampsilis mantle is modified to look like fish and when fish comes to eat it clam squirts glochidia into mouth of fish * once attached to fish will stay there for about three weeks then drop off and go to bottom and develop into adult SQUID, OCTOPUS AND CHAMBERED NAUTILUS * ABOUT 650 LIVING SPECIES, 8000 FOSS

IL SPECIES * Most highly evolved molluscs; probably evolved from a monoplacaphoran-like ancestor * the whole class has adapted to swimming * there are a series of tentacles (arms) which are homologous to the foot of other molluscs * have suckers- adhesives cups * well developed head with very well developed eyes * body elongated on a dorsoventral axis * tentacles and head at anterior end of body * visceral mass is posterior * largest of all the invertebrates; giant squid are known to have reached a length of 16 meters (50 feet) including tentacles; tentacles alone can be 6 meters * some circomstantial evidence of sucker scars on whatles lead scientists to believe they may even get bigger * Octopi don't get nearly as large as squid; * largest species with tentacles and all gets about 5 meters long; but body is only 40 cm in diameter * all live in dens - crevises in rocks * in this class the shell is very reduced and almost lost; the only group with well developed shells are either extinct (Ammonites) or belong to the nautili (chambered and paper) * shell here is perforated and

 divided by septa each has a hole (siphuncle)- which acts in balancing pressure inside shell when nautilus changes depth * In squid and cuttlefish shell is reduced and internal (pen) and is pliable and plastic in nature; in octopi it is totally lost

Question: Snails, squid, clams, scallops, mussels, etc., all belong to which phylum?
Answer: Molluscs